Blood lactate has been used to determine the aerobic capacity and long distance performance. Recently, a new methodology has been suggested to supplant the invasive blood lactate techniques. Salivary lactate has received attention because it shows high correlation to blood lactate in progressive overload test. We evaluated the correlation between salivary and blood lactate during a long distance run and assessed possible changes in salivary lactate concentration. Fifteen expert marathon racers ran 30 km as fast as possible. Saliva and 25 muL of blood were collected at rest and at each 6 km for lactate determination. Blood lactate concentration increased in the 6th km and then remained constant until the end of the race. Salivary lactate increased after 18 km in relation to basal. We found high correlations between blood and saliva absolute lactate (r=0.772, p<0.05) and the blood lactate relative concentration corrected by protein (r=0.718, p<0.05). The highest correlation found between absolute and relative salivary lactate was r=0.994 (p<0.001). Our results show that it is possible to use salivary lactate with absolute values or relative protein concentration. In addition, salivary lactate showed a high correlation with blood lactate in endurance events.